Dental plaque was collected from monkeys (Macaca fasciularis) which had been maintained on a high or low sucrose diet and had different levels of caries. Significant amounts of dextranase activity were measured in all dental plaque fluids. Levels of enzyme activity did not appear to be related to caries experience in the animals. The major dextranase activity in plaque fluid appeared to be elaborated by oral bacterial other than S. mutans, serotype g. Several dextranase producing bacteria, including S. mutans, serotype c and S. sanguis type II, have been isolated from monkey plaque. Characterization of the biochemical and immunological properties of the destranases from these bacteria isolates is in progress.